Fiberglass insulation question?

[plout99]

Fiberglass HVAC insulation or wall insulation question?

Is there any difference in fiberglass unfaced hvac duct insulation and typical unfaced residential fiberglass wall insulation? My googling shows hvac using the same astm standards for r value, flame spread and smoke as residential wall insulation. I ask because I found a deal on r8 Johns Manville flex-glass for heat ducts that will let me do all the walls with 3 layers in my 32x48x14 pole barn for $ 420. About a third of any other options I have considered. I emailed Johns Manville no answer yet, I don’t think they will endorse it being used for walls since that wasn’t it’s designed purpose. Doesn’t mean it wont work though.

 

[egdede]

For about 66% in savings, in a pole barn I wouldn't even ask. But, next thing you know someone will explian the difference.

 

[plout99]

Thoughts anyone.

 

[egdede]

Someone will help you out I am sure. What I do know is that some/many manufacturers of fiberglass wall insulation claim they address sound transmission now (somehow; I don't know how). If that is the difference, less of a concern in a pole barn.

 

[Jking24]

I don't know much about how they rate it but it's designed to be used in the same space so i see no problem with it at all. I also didn't know they made duct insulation unfaced

 

[Mattlt]

I think the only possible drawback is if the 3 layers were to separate from each other. Maybe that's not a bad thing either? Trapped air is still an insulator. Assuming those layers would fill up the stud cavity?

 

[SGKent]

we have R6 on the ducting. Every time the system turns on it brings in a shot of attic temp air even if it was only sitting 20 minutes. When I was younger and more nimble, I wrapped the old ducts with R13 many years ago, and they would stay consistent temp for half a day. I don't think money on R8 would be well spent as the main wall insulation.

 

[plout99]

we have R6 on the ducting. Every time the system turns on it brings in a shot of attic temp air even if it was only sitting 20 minutes. When I was younger and more nimble, I wrapped the old ducts with R13 many years ago, and they would stay consistent temp for half a day. I don't think money on R8 would be well spent as the main wall insulation.

There would be three layers of r8 for a value of r24 which will be slightly reduce do to compression of the layers.

 

[plout99]

I think the only possible drawback is if the 3 layers were to separate from each other. Maybe that's not a bad thing either? Trapped air is still an insulator. Assuming those layers would fill up the stud cavity?

They will fill the cavity and be slightly compressed which will reduce the cumulative r24 but not a lot. The compression should eliminate any separation problems I would think.

 

[NUTTSGT]

I cut apart some insulated flexible duct to wrap it around a regular metal duct. It looked like the same thing as wall/ceiling insulation to me.

At 1/3 of the cost, I'd use it. It might be more labor intensive, but that's sweat equity. You're leaving more cash on the table to use elsewhere.... like metal for the ceiling.

 

[CTyankee]

I doubt there is any difference, but I am surprised the cost is that much cheaper than doing it with reg batts.

 

[egdede]

If you really want to punish yourself, get an insulation knife. You could filet the panels sandwiched between plywood so that you are using 2 1/2 panels at full loft with a 15% lower cost per square'.

No matter what precautions you take, you'll itch.